QA·C Help - 0313

	0313	Casting to different function pointer type.

Pointers		REFERENCE - ISO:C90-6.3.4 Cast Operators - Semantics

An expression of type 'pointer-to-function' is being cast to a different 'pointer-to-function' type.

According to ISO:C90, the only circumstances under which a function pointer can legitimately be converted to a different function pointer type are as follows:

"A pointer to a function of one type may be converted to a pointer to a function of another type and back again; the result shall compare equal to the original pointer. If a converted pointer is used to call a function that has a type that is not compatible with the type of the called function, the behavior is undefined."

The circumstances under which such conversions should be necessary are not common.

For example:


/*PRQA S 0428,2017,2211,3198,3199,3203,3408,3447,3635,3672 ++*/


extern void error( long * x );

extern void foo(void)
{
    void (* pf)( int * x );
    unsigned long ulx;

    pf = (void (*)( int * x)) error;              /* Message 0313 */

    ulx = (unsigned long)&error;                  /* Message 0305 */

    pf = (void (*)( int * x)) ulx;                /* Message 0305 */

}

MISRA-C:2004 Rules applicable to message 0313:

Rule 11.1 (Required)

Conversions shall not be performed between a pointer to a function and any type other than an integral type.